1. Field of the Invention
The present general inventive concept relates to an image forming apparatus and a method of controlling the same. More particularly, the present general inventive concept relates to an image forming apparatus and a method of controlling the same, which print a color image by superimposing the color image on a transfer medium and transferring the superimposed color image to a printing medium.
2. Description of the Related Art
An electro-photographic image forming device generally includes a photosensitive medium, for example, a photosensitive drum, for developing an image, and a traveling belt, e.g., an intermediate transfer medium, for transferring the image developed on the photosensitive drum to a printing paper. A developing unit for each color is arranged on one side of the photosensitive drum so as to develop images for four colors, i.e., yellow, magenta, cyan, and black, on the photosensitive drum in sequence.
As one example of the intermediate transfer medium, an intermediate transfer belt is driven in contact with the photosensitive drum. A color image developed for each color is superimposed on the intermediate transfer belt from the photosensitive drum to obtain an image for a desired color, and then the final color image formed by the superimposition is transferred to a recording medium which is moved in contact with the intermediate transfer belt.
The intermediate transfer belt is driven in one direction, with it being supported by a plurality of support rollers comprising a drive roller and a tension roller, to serve a function of transferring the superimposed color image to the recording medium.
In the above construction, a cleaning blade is positioned in contact with the intermediate transfer belt so as to clean toner remaining on the intermediate transfer belt.
If the intermediate transfer belt is driven at a warming up or printing operation in the state that the cleaning blade is in contact with the intermediate transfer belt, the cleaning blade may be turned over due to the friction therebetween. In order to prevent the turn-over of the cleaning blade, a toner band to prevent the turn-over of the cleaning blade is usually provided on the intermediate transfer belt at a predetermined width.
In particular, during the printing operation, the toner band is applied in an interval between the color images (whole or specified period) to prevent the turn-over of the cleaning blade.
Since the toner band applied at the warming up operation secures a time needed to sufficiently stabilize a potential of the photosensitive drum prior to exposure of an exposing unit for image forming, potential variation of the photosensitive medium is reduced and/or eliminated. The toner band applied at the interval between the color images does not secure a time required to sufficiently stabilize the potential of the photosensitive drum, however, which impacts a next image by causing an exposing potential variation of the photosensitive drum. Thus, there is a problem that a so-called dark band is formed on the image.
Referring to FIG. 1, a yellow image is firstly formed in a period Y, and a magenta image is formed in a period M. Accordingly, the toner band is applied at the interval between the yellow and magenta image forming periods Y and M. In order to apply the toner band, the photosensitive drum is exposed with a predetermined potential in a desired period I between the yellow and magenta image forming periods Y and M. A potential variation is produced on the photosensitive drum between the exposed portion and a predetermined portion A of the next magenta image forming period M. More specifically, the exposing potential is lower in the toner band forming period I, compared with other periods. As a result, since an amount of the toner is varied (i.e., it is increased), a horizontal dark line or dark band occurs on the image.
Also, the image forming device is provided with a cleaning unit for cleaning the photosensitive medium, in addition to the cleaning unit for cleaning the transfer medium such as the intermediate transfer medium. Accordingly, a toner band is applied on the photosensitive medium to provide lubrication between the cleaning unit for the photosensitive medium and the photosensitive medium. Accordingly, since the exposing potential is also varied on the photosensitive medium, the dark line described above occurs on the image.